The present invention has to do with improvements in that old and common form of dial torque wrench which is the subject matter of and is disclosed in my U.S. Pat. No. 3,726,134 for DIAL TORQUE WRENCH issued Apr. 10, 1973. The disclosure of the above noted patent is incorporated herein by reference.
The above-noted prior art wrench structure has been made and sold for in excess of fifteen years and has attained notable commercial success. The accuracy and dependability of that wrench structure has been equal to or superior than all known competitive wrench structures of a similar class. While the foregoing is true, it has long been recognized that the accuracy of that wrench diminishes markedly as forces applied through it are increased and approach the upper end of the operating range of the wrench. Another shortcoming found to exist in the noted prior art wrench resides in the frequent inability of the users of the wrench structure from gaining an effective viewing angle of the dial face and pointer so as to avoid inaccurate reading of the dial as a result of adverse parallax conditions.
Until recently, the above noted shortcomings in the noted prior art wrench have been considered to be inherent in the mechanics and/or dynamics of the structure and have been accepted as "givens" (in the vernacular).
In the recent past, as a result of ever-increasing demands for greater accuracy that threaten to adversely affect the utility of that wrench in certain industries and throughout important areas of the marketplace, repeatd detailed studies of that wrench structure have been undertaken. Those studies have disclosed that the principle cause of inaccuracies in that structure are caused by normally imperceptible, improper pivotal movement and swinging of the cantilever-supported operating rod that extends from the work-engaging head to the dial mechanism.
The noted cantilever-supported elongate operating rod in the noted prior art wrench structure functions to multiply slight lateral deflection of the beam and corresponding movement of the work-engaging head, in whichever direction the deflection beam might be deflected. Due to its great length, the operating rod tends to multiply deflections of the beam to such a degree that slight irregularities in deflection of the beam appear as major errors at the dial face of the dial means. For example, it has been determined that, due to the right angular relationship of the work-engaging head relative to the longitudinal axis of the deflection beam and the lever effect afforded thereby, upon normal use and operation of the wrench structure, the beam is not only deflected laterally (as intended) but is also subjected to what has been determined to be substantial torsional deflection. To the best of my knowledge and belief, the degree of torsional deflection of the deflection beam and resulting adverse displacement of the work-engaging head when bench testing that structure was so slight that it was never before recognized as presenting a meaningful factor and was summarily dismissed and/or ignored. In point of fact, it has been found that in regular field use of that structure, such torsional deflection of the deflection beam is often a major factor in imparting notable inaccuracies in that wrench structure which heretofore were believed to be brought about by the accumulated effect of irregularities built into the wrench structure, in spite of tight quality controls.
In addition to the foregoing, in normal use of the noted prior art wrench, the work-engaging head is subjected to great torsional forces and is often torsionally deflected to an extent to cause major misalignment of the operating rod and substantial error in the force indicated by the dial mechanism.
The two above-noted causes for error, though each might cause minor adverse effects, the effects of both are cumulative and such that substantial adverse effects are caused thereby.
It was determined that if the effect of torsional deflection of the head and the deflection beam in the above-noted prior art wrench structure was, for example, reduced by about 25%, the accuracy, effectiveness and utility of the resulting wrench structure would be materially greater than the noted prior art wrench structure and the resulting wrench would dependably meet or exceed those requirements for accuracy that are now in effect and those requirements that are likely to be implemented in the foreseable future.